PROJECT SUMMARY It is estimated that more than 240 million people are living with HBV infection and more than 36 million people with HIV infection worldwide, of which up to 60% of HBV-infected and 30% of HIV-infected individuals are unaware of their infection status. HBV coinfcetion in HIV-infected patients is linked to increased risk of cirrhosis and Hepatocellular carcinoma (HCC), higher rate of chronicity and occult HBV, and higher rate of liver-related morbidity. Accurate and timely knowledge of HBV/HIV coinfection status is essential to select the optimal ART regimen and tenofovir disoproxil fumarate (TDF) as well as treatment monitoring to identify if treatment switch is required. Previous studies showed that simultaneous detection of HIV and HBV using on-site POC tests can significantly improve the screening process and linkage to care for individuals at high risk for chronic viral infections. In addition, the undiagnosed, untreated, infected individuals can play a significant role in infection transmission to others. If untreated, the infection can lead to advanced stages, which increases the risk of mortality. The lack of appropriate diagnostic tools especially for people at high risk of infection is one of the reasons for the infection unawareness. The development of point-of-care (POC) multiplexed diagnostics is crucial in expanding hepatitis testing and disease management services for individuals with HIV/HBV co- infection in a timely manner. Viral load testing is the most accurate and preferred approach for HIV and HBV detection and treatment monitoring. Nucleic acid-based assays are currently used for viral load testing for disease diagnosis and treatment efficacy monitoring, however, these assays are still relatively expensive, laboratory-based, and technically complex. Multiplexing HIV/HBV using nucleic acid-based methods is also challenging due to simultaneous detection of RNA (HIV) and DNA (HBV) target molecules. Furthermore, current POC rapid tests (dipsticks) target antibodies/antigens against HIV/HBV generated after infection, cannot detect treatment failure and acute infection, and have low sensitivity/specificity. Thus, to increase access to HIV/HBV care with regular treatment monitoring and to improve treatment outcomes, there is an urgent need for inexpensive, rapid, sensitive, and specific HIV/HBV viral load testing tools at the POC. The main goal of this highly interdisciplinary project is developing a portable nanotechnology-empowered cellphone-based system for rapid (<30 minutes) multiplexing HIV/HBV in fingerprick volume (<100 L) of whole blood placed on an inexpensive (<$2), disposable, and mass-producible microfluidic device. In our proposed method, (i) target viruses are captured on-chip using highly specific envelope antibodies, (ii) captured viruses are labeled with Pt nanoparticles conjugated with respective antibodies, (iii) Pt-labeled captured viruses generate bubbles through gas formation of Pt nanoparticles in the presence of hydrogen peroxide on-chip, (iv) the bubbles can be quantified using a low-cost (<$4) cellphone optical attachment for quantitative/qualitative viral load testing.